1. Field of the Invention
The present invention relates to a semiconductor wafer inspection apparatus which detects defects (including scratches, dust, and cracks) at the outer peripheral portion of a semiconductor wafer (hereinafter referred to as a “wafer edge portion.”
2. Description of the Related Art
Normally, semiconductors are manufactured by executing steps described below, and defect inspection is executed in each manufacturing step. In the pre-process of semiconductor device manufacture, an oxide film (SiO2) is formed on the surface of a semiconductor wafer (hereinafter referred to simply as a “wafer”), and then a thin silicon nitride film is deposited on the oxide film.
Then, a photolithography step is carried out to form a thin film of photoresist (photosensitive resin) on the surface of the semiconductor. Subsequently, an adequate amount of rinsing liquid is dropped onto the wafer edge portion of the wafer, and the photoresist is removed from the wafer edge portion of the wafer by an amount corresponding to a predetermined width.
Then, processing using an exposure device, such as a stepper, is executed. That is, ultraviolet rays are guided to the photoresist-coated wafer by way of a mask corresponding to a semiconductor circuit pattern, so that the semiconductor circuit pattern is transferred onto the photoresist. Then, developing is executed. For example, the exposed photoresist is dissolved in a solvent, thereby leaving the not exposed resist pattern.
Then, the oxide film and silicon nitride film formed on the surface of the wafer are successively subject to selective removal (etching), using the resist pattern remaining on the surface of the wafer as a mask. The resist pattern is then removed from the surface of the wafer by ashing (resist separation). The resultant wafer is cleaned of impurities.
In the semiconductor manufacturing process described above, defect inspection is carried out in each manufacturing step. In the defect inspection, the surface of the semiconductor wafer is mainly inspected to see if there are scratches, dust, cracks, stains or uneven portions. In recent years, the observation of the edge cut amount, the distribution, etc. of the wafer is required. In particular, it should be noted that cracks result in the breaking of the wafer itself. This being so, the presence or absence of cracks at the wafer edge portion has to be detected as early a step as possible to determine whether the wafer is good or bad.
A technique for inspecting a wafer edge portion is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 9-269298. According to this technique, a collimated beam condensed by an elliptic mirror is guided to the edge portion of a wafer. Of the diffracted light obtained thereby, the low-order components are shielded so that the elliptic mirror condenses high-order components of the diffracted light. On the basis of the intensity and/or the frequency components of the diffracted light, a defect at the wafer edge portion or the property of the wafer edge portion is identified. A technique for allowing a focal position to be located inside a wafer and enabling detection of diffused light coming from inside the wafer, is also known in the art, as seen in Jpn. Pat. Appln. KOKAI Publication No. 2000-46537. Furthermore, a technique for irradiating the edge portion of a wafer with an infrared laser beam and examining the wafer by means of at least one video camera by slanting the wafer relative to the laser beam, is also known in the art, as seen in Jpn. Pat. Appln. KOKAI Publication No. 2000-136916.
Although the techniques described above enable detection of the edge portion of a wafer, they in no way detect a defect at that wafer edge portion, especially an edge cut line width. For this reason, the processing in the steps that follow the formation of a thin photoresist film may give rise to a defective wafer or other undesirable results.
For defect inspection, image data (an edge image) on the entire outer circumference of a wafer has to be acquired. In the above technologies, however, the edge image of the entire circumference is not acquired, and the entire circumference of the wafer edge portion of a semiconductor wafer is not examined for defect detection.
An object of the present invention is to provide a semiconductor wafer inspection apparatus which can easily inspect the outer circumference of a semiconductor wafer in a short time in a semiconductor manufacture inspection process.